Until the third level, the game is easy. But when the third stage starts, it's a pain.
Those Igor enemies are the worst thing you can find in this game and yes, Frankenstein is one of the hardest boss of the game (because that damned Igor that throw fireball every single moment).
Then, there's Death. But passing the corridor before reaching it, it's a pain. All the Medusa heads, the armored knight...the first time I managed to pass easily that section using the stop watch, but then Death kills me in two seconds.
After that, I acquired the boomerang, but passing that corridor was a nightmare :|
Dracula stage, otherwise, is very easy, except that Igor part with flying birds. The boss itself is easy (jump, hit its head, repeat), when he turns into a monster, I simply throw him all the boomerang I have, hitting him with whip.
But the game is hard, yes.